In an analysis using a gas chromatograph, the compound to be analyzed is sometimes converted into a derivative that is easier to analyze or detectable with higher sensitivity, if the compound as is cannot be detected at all or is detectable only with low sensitivity and accuracy. Conversion of a compound into a derivative uses a reagent that causes various kinds of chemical reactions with a functional group of the compound to be analyzed. Examples of the derivation process are silylation, alkyl-esterification, acrylation and dimethylsilylation.
Derivation of a sample containing a target compound generally includes the following steps: initially, a dry nitrogen gas is sprayed onto a liquid sample as is, or after being concentrated, to vaporize the sample and dry it on the inner wall of a container, such as a test tube or a vial; a predetermined derivation reagent solution is put into the container and mix it with the sample; and the mixture is left at rest for some time to obtain a derivative of the target compound contained in the sample.
Such a manual derivation process consumes time and labor because it requires the liquid sample to be once vaporized and dried. Accordingly, the throughput of the gas chromatograph analysis deteriorates if the derivation process is performed; it will take a very long time if there are a large number of specimens to be analyzed. Also, even if there are only a small number of specimens, the time-consuming method is hardly available in some special cases, such as a test for illegal drugs where the test result should be quickly obtained. Thus, to enhance the throughput of a gas chromatograph analysis including a derivation process still remains a big challenge.
Also, the conventional method is accompanied by the troublesome work of preparing tools for spraying the dry nitrogen gas, for mixing the sample and the derivation reagent, and for other operations performed for the derivation process. Moreover, many reagents require careful handling: some are harmful to humans (i.e. poisonous or deleterious), and some are highly flammable. This requirement limits the scope of people available for this job. It also demands adequate attention to the ventilation and other working conditions. For such reasons, the derivation technique is not actively used in the gas chromatograph analysis except in the case where the derivation is indispensable.
Some conventional apparatuses are provided with an automatic mechanism intended to eliminate troublesome manual work for the derivation process. For example, the Japanese Unexamined Patent Publication No. 2001-337078 discloses a gas chromatograph having an automatic pre-treating function for automatically performing a pre-treatment including the derivation process. However, this conventional apparatus requires plural thermostatic chambers, a channel selector valve and other devices, which inevitably makes the apparatus large and complex. Therefore, its production cost is higher than that of ordinary gas chromatographs.
To solve the above-described problems, the present invention provides a simple and inexpensive sample injector for a gas chromatograph, which is capable of improving the throughput of the analysis by reducing the time and labor for the derivation process.